Abstract:

Genetic differences between early and late forms of
Alaskan chinook salmon (Oncorhynchus tshawytscha) were
identified using two genetic approaches: mitochondrial
DNA (mtDNA) analysis and protein electrophoresis. The
study populations consisted of early- and late-run chinook
salmon in each of the Kenai and Kasilof rivers in Alaska,
and a single population from the Minam River, Oregon, that
provided a relative scale for the differences among the
Alaskan populations. Two segments of mtDNA were amplified
separately using the polymerase chain reaction (PCR) and
then digested with 14 to 16 restriction enzymes. Results
showed that the two early runs were genetically similar to
each other but different from either of the late runs.
The late runs were different from each other based on the
frequency of the common haplotypes. The Minam River stock
shared two haplotypes with the Alaskan stocks and
displayed one unique haplotype. The frequency difference
in the shared haplotypes together with the presence of a
unique haplotype allowed us to separate the Oregon
population from those in Alaska. In the protein analysis,
each of the five populations was examined at 30 allozyme
loci to determine variation within and between the runs.
Based on 14 polymorphic loci, Minam River chinook salmon
were genetically distinct from the Alaskan populations.
Within the Alaskan populations, the two early runs were
most similar to each other but different from the two late
runs; the two late runs were also genetically most similar
to each other. Based on all loci, protein electrophoresis
proved to be a useful technique to separate stocks of
chinook salmon. On a locus by locus basis, however, mtDNA
was more powerful. Both mtDNA and allozyme analysis
suggest that chinook salmon may segregate into genetically
different early and late forms within a drainage.